Many approaches are used to whiten teeth. One common approach uses abrasives (for example, in toothpastes and prophyaxis pastes) in combination with a polishing action to polish discolorations and stains off of the surface of the teeth. Because abrasives only work on the surface of the teeth, the intrinsic color of the teeth is largely unchanged. As such, abrasives only offer limited effectiveness in whitening of the teeth.
Another approach is the use of chemical whitening actives in a composition to intrinsically and extrinsically whiten teeth. A chemical whitening active is applied to the teeth for a period of time to allow the active to act upon the teeth and provide an improvement in the whiteness of the teeth. Whiteners are commonly applied to the teeth using toothpastes, rinses, gums, floss, tablets, strips and trays. A common chemical whitening active is peroxide. Often, strips and trays are used to apply peroxide for contact times beyond that achievable with typical toothbrushing. Concentration of the whitening active, contact time and number of applications are some of the primary parameters which dictate the rate and amount of whitening achieved with peroxide based tooth whitening compositions. Whitening products using a strip of material in combination with a chemical whitening active are described, for example, in U.S. Pat. Nos. 5,891,453 and 5,879,691, the disclosures of which are incorporated herein by reference. The whitening composition described therein can include a peroxide active.
Efforts to increase the whitening efficacy of products in order to deliver a more satisfying product experience have included increasing the concentration of peroxide for a faster whitening per time of use. Maintaining the peroxide on the tooth surface for longer contact times and/or for an increased number or frequency of applications have also been employed for increased whitening. While increasing concentration, increasing wear time and increasing number of applications can be effective methods of achieving higher degrees of tooth whitening from a tooth whitening product, each of these parameters also may have a negative impact on the consumer's experience.
Increasing the concentration of the peroxide in the whitening composition, holding all other parameters essentially constant, can produce more tooth sensitivity and cause more soft tissue irritation. Sufficiently high concentrations of peroxide may require a physical barrier, such as a rubber dam, to prevent the peroxide from contacting and burning the soft tissue thereby making the use of the high peroxide concentrations inconvenient and impractical for unsupervised at home and repeated use. In fact, even conventional in-office tooth whitening compositions having a peroxide concentration equivalent to as low as 13% hydrogen peroxide, often utilize a rubber dam to protect the soft tissue during the bleaching process. Increasing the use time and/or frequency generally increases the amount of tooth sensitivity and gingival irritation as well as make the product more inconvenient to use.